1. Field of Invention
This invention relates to an improvement in the plastic tab closures used for closing the necks of plastic bags that are commonly employed in containing breads, produce, refuse, and the like.
2. Description of Prior Art
Grocery stores and supermarkets commonly supply polyethylene bags to consumers for the containment of items of produce. Such bags are also commonly used as packaging by suppliers in order to provide a resealable container for bread and other items, both edible and inedible.
Originally, these bags were sealed by the supplier with staples or by heat, but consumers objected to such methods of closure since they were of a rather permanent nature in that the bags could be opened only by tearing them, thereby damaging them and rendering them impossible to reseal.
Thereafter, inventors created several types of closures to seal plastic bags in such a way as to leave them undamaged after they were opened. U.S. Pat. No. 4,292,714 to Walker (1981) discloses a complex clamp which can close the necks of bags without causing damage upon opening; however, these clamps are prohibitively expensive to manufacture. U.S. Pat. No. 2,981,990 to Balderree (1961) shows a closure which is of expensive construction, being made of PTFE, and which is not effective unless the bag has a relatively long "neck"; thus, if the bag has been filled almost completely and consequently has a short neck, this closure is useless. Also, being relatively narrow and clumsy, Balderree's closure cannot be easily bent by hand along its longitudinal axis. And finally, his closure does not hold well onto the bag but has a tendency to snap off.
Although twist closures with a wire core are easy to use and inexpensive to manufacture, do not damage the bag upon being removed, and can be used repeatedly, nevertheless they simply do not possess the neat and uniform appearance of a tab closure, they become tattered and unsightly after repeated use, and they do not offer suitable surfaces for the reception of print or labeling. These ties also require much more manipulation to apply and remove.
Several types of thin, flat closures have been proposed--for example, in U.K. patent 883,771 to Britt et al. (1961) and U.S. Pat Nos. 3,164,250 (1965), 3,417,912 (1968), 3,822,441 (1974), 4,361,935 (1982), and 4,509,231 (1985), all to Paxton. Although inexpensive to manufacture, capable of use with bags having a short neck, and producible in break-off strips, such closures can be used only once if they are made of frangible plastic since they must be bent or twisted when being removed and consequently will fracture upon removal. Thus, to reseal a bag originally sealed with a frangible closure, one must either close its neck with another closure or else close it in make-shift fashion by folding or tying it. Although my own U.S. Pat. No. 4,694,542 (1987) describes a closure which is made of flexible plastic and is therefore capable of repeated use without damage to the bag, nevertheless all the plastic closures heretofore known suffer from a number of disadvantages:
(i) Their manufacture in color requires the use of a compounding facility for the production of the pigmented plastic. Such a facility, which is needed to compound the primary pigments and which generally constitutes a separate production site, requires the presence of very large storage bins for the pigmented raw granules and presents great difficulties with regard to the elimination of the airborne powder which results from the mixing of the primary granules.
(ii) If one uses an extruder in the production of a pigmented plastic--especially if one uses only a single extruder--a change from one color to a second requires purging the extruder of the granules having the first color by introducing those of the second color--a process which, until purging is complete, inevitably produces, in sizeable volume, a product which is of intermediate color and must be discarded as scrap, thereby resulting in waste of material and of production time.
(iii) The colors of the closures in present use are rather unsaturated. If greater concentrations of pigment were used in order to make the colors more intense, the plastic would become more brittle and the cost of the final product would increase.
(iv) The use of pigmented plastic closures does not lend itself to the production of multicolored designs, and it would be very expensive to produce plastic closures in which the plastic is multicolored--for example, in which the plastic has stripes of several colors, or in which the plastic exhibits multicolored designs.
(v) Closures made solely of plastic generally offer poor surfaces for labeling or printing, and the label or print is often easily smudged.
(vi) The printing on a plastic surface is often easily erased, thereby allowing the alteration of prices by dishonest consumers.
(vii) The plastic closures in present use are slippery when handled with wet or greasy fingers.
(viii) A closure of the type in present use can be very carefully pried off a bag by a dishonest consumer and then attached to another item without giving any evidence of such removal.